Electrodes used for EKG (electrocardiogram), EEG (electroencephalogram) and EMG (electromyogram) recordings are traditionally surface electrodes and these are commonly known as standard or conventional electrodes. These conventional electrodes are either simply metal plates connected by wires or plastic discs coated with silver chloride (AgCl). A patient's skin surface requires prepping by scrubbing, e.g., with sandpaper, to remove any dead tissue, hair or any oil that might increase the resistance between the electrode surface and the tissue. The electrodes are often attached to a patient's skin using adhesive tapes. Often conductive gel is applied to the electrode surface prior to attaching to the patient's skin to improve conductivity. It is essential to have good conduction between the electrode and the patient's skin to get good electrogram recordings. The conventional electrodes have about 400Ω to 1500Ω resistance.
Microneedle electrode arrays are generally made by etching the silicon wafers (described in U.S. Pat. No. 6,256,533 by Yuzhakov et al.) and electroplating them with conductive materials like gold. This is an expensive way of making the electrodes. These are traditionally used in labs for experimental purposes only. There are even smaller scale needle arrays made (described in U.S. Pat. No. 6,334,856 by Allen et al.) for drug delivery applications, etc. There are hollow microneedle array devices (described in U.S. Pat. No. 6,603,987 by Whitson) to pierce the skin into the hypodermis layer to draw blood samples and similar devices described in U.S. Pat. No. 6,611,707 by Prausnitz et al. for the drug delivery applications.
Biowave Corporation has introduced a Percutaneous Electrode Array to be used with a Percutaneous Neuromodulation Pain Therapy System and the design of the electrode is described in U.S. Pat. Nos. 7,013,179 and 7,130,696 by Carter et al. The microneedle array is adhered to a hydrogel adhesive layer and the impedance is about 1500Ω. This electrode would not improve signal quality for EKG, EEG and EMG recordings.
A microneedle array patch is disclosed in U.S. Pat. No. 7,658,728 by Yuzhakov for a drug delivery application and the needle array is electrochemically machined and needles are bent. This device in its state can't be used for EKG, EEG and EMG recordings.
There is a need for an electrode with low impedance that provides good electrode-tissue contact with the ability to maintain that good electrical contact for an extended period of time.